Tuning arrangement for cavity resonators



July13, 194s. J. c. SLATER. 2,445,282

TUNING ARRANGEMENT FOR CAVITY RESONATORS Filed May 19, 1944 FIG. 2

INVENTOR J. C. SLATER ATTORNEY 4 UNITED:

Patented y 3, 1948 i::.:.:;.;-.-

4 2,445,2saf,

'TUNZING ARRANGEMENT FOR CAVITY RESONATORS.

John C. Slater, Cambridge, Mass, assignor, to" QBell Telephone Laboratories, Incorporated,

New York, N. Y., a corporation of New York Es PATENT" OFFiC-E.

I 5 Applicants May 19, 1944, Serial No. 556,298

volving the handling of microwaves, as in the generation and transmissionof such .w'aves. It is customary where power outputs of several kilowatts are required to generate microwaves in a magnetron oscillator which has a rfiSQnator containing one or more cylindrical resonating cavities. While. the oscillating system of. the magnetron may be predesigned to operate approximately at a desired frequency, itis useful to be able to adjust the operating frequency after. the oscillator has been connected toa transmission system. One reason for this is that-the operating frequency of a systernmade vup ofan oscillator and aload, which system may also include an intermediate transmission medium therebetween, depends not alone upon the dimensions of the oscillator but also upon the impedance offered to the oscillator by the load and by any such transmission medium. Oscillators have in certain cases been produced in quantity, inspected and tested in a standardized transmission cir- .cuit and those oscillators operating outside a prescribed frequency bandjhave been rejected as unsatisfactory. Of, the oscillators passing such a test moreover, some operate' in the testlcircuit at a frequency close to one edge of the band. Such marginal oscillators when placed in the systemjfor which they are ultimately intended,

which system'may differ somewhat from the test circuit in its impedance characteristics, may operate at a frequency outside the band limits,

and thus be unsatisfactory. An oscillator'which is-oif frequency usually 'canbe brought 'to operf' Claims. (01. 315-39 2 the known means may be limited to producing insufiiciently large changes in the resonant frequency or may be unsuited electrically or mechanically for the particular application in which it is desiredto have a frequency adjustment.

The tuning arrangement of the present invention is particularlyadapted to acurrently preferred type of multi-anode magnetron having a perforated anode block containing aplurality of circular cylindrical resonating cavities with their axes parallel to the axis of a central cylindrical interaction space. In accordance with the in- ,ventlon, one of the resonating cavities is. ex-

.tended radially outwardly with reference to the interactionspace to form a parallel platetransmissionline. A tuning bridge is provided which connects the plates of said line and .is slidable radially with reference to the central interaction space. vThe transmission lineand the tuning bridge preferably eachextend axially substantially the full length of the resonating cavity, or in other'words from end to end of the anode block. Mechanical means are shown, for adjust- 7 ing the position of the tuning bridge.

In the drawing, U

, Fig. Us a perspective view, partly broken away, showing a magnetron oscillator embodying the invention; and, 1

Fig. 2 is a cross-sectional view of a portion of the structure of Fig. 1, showing the tuning element in a different position from that shown in Fig. 1.

Referring to the figures, the anodeblock I0 ofa magnetron is shown with its enclosin case comprising a cylindrical side Wall portion II and end plates Hand [3, respectively. The central cylindrical interaction space of the magnetron is. shown at [4 and has mounted along its central axis a cathode l5 which may be suitably supported as by means of sufiiciently rigid wires or rods 16 and H which are brought. through 'the'wall portion II and supported by sealing means such as glass beads l8 and I9, respectively. A plurality of resonating chambers 20 may be provided as in the form of cylindrical perforations of the anode block ill the cylinders having their axes parallel to the axis of the interaction space [4. The individual resonating cavities 26 may be connected to the interaction space M by means of coupling slots or channels 2| extending from end to end of the anode block [0. One of the resonating cavities 20 may be provided with a coaxial line output fitting comprising an outer sheath 22 and an inner conductor 23, the latter terminating in a coupling loop 24 within the chamber in accordance with well-known practice. The anode block l0 may be composed of conductive material or at least the surfaces of the perforations should be conductive to a sufficient depth to serve as reflectors of electromagnetic waves of the generated frequency.

In accordance with the invention, one of the chambers such as that designated in the drawing, is enlarged by being extended radially. to

form a parallel plate transmission line havingplates or conductive surfaces ZB-and 27; respectively, as by a slot extending from end to end, of the anode block. A tuning bridge 28 is slidably mounted between the plates or surfaces-"2E and 21, the bridge 28 preferably extending'finjthe axial direction the full distance from 'endto end of the anode plate I0. The :slot'in which-the tuning bridge slides may be described, as atuning slot, and in the embodiment shown; the tuning slot has a width substantially the diameter of the cavity 25.

Any suitable means may be employed for adjusting the radial position of thebrid'ge 28in the tuning slot, preferably from outside the Vacuum chamber of the magnetron. Illustrative of such 'meansis the arrangement shown in the drawing inwhich a box-like extension-29 is formed upon the wall portion ll oppositethe resonating cavity 25, the vertical walls of the box 29 being preferably formed-as extensions of the surfaces 26 and 21, To guide the motion of the tuning bridge 28, there may be provided a block 30 fitted snugly inside the box 29 and attached to the bridge28 as shown. The block-30 and bridge28 maybe moved together by means of a r'od 3|. To allow for the motion of the rod 3| while at the same time preventingloss of vacuum in the vacuum chamber of the magnetron, the outer end of the rod 3| may be passed through and sealed to a bellows 32 preferably of metal. The rod 3| may pass through a clearance hole 33 in the outer endof the box 29, the bellows 32 having-its inner edge fastened and sealed around the hole '33.- Suitable means such as a thumbscrew 34 coupled to-the rod 3| through a ring 35 and a rotatable joint 36 may be provided for controlling the motion of the rod 3|,

The thumb screw 34 maybe supported as by a bracket 31 secured to the wall II.

It will be evident that rotation of thethumb screw 34 will cause axial motion 2 of "the rod 3 I which will in turncause axial motion of th tuning bridge 28 to vary the position of the'bridge 28along the parallel plate transmission-line comprising the surfaces 2B-and 21. The limits of'motion of the tuning'birdge 28 maybe chosen as desired, the innermost limit, in'the arrangement illustrated, being determined by the striking-"of the tuning bridge against the circular cylindrical surfac of the cavity25,and the' outer'limit' by the striking of the block 30' against the outer Wall of'thebox 29. It will be evidentthat the travel of the tuning bridge 28 may extend over a considerable portion of a wavelength of the operating frequency or even over one or more complete wavelengths, thus providing for a relatively large frequency adjustment.

What is claimed is: I

1.; A tunable. cavity, resonator? device. comprisingwa perforated cylindrical block of conductive material, the perforations of which include a cylindrical interaction space, and a plurality of ':,cylindricalicavity resonators surrounding said "reaction space and spaced therefrom, a central axis of said interaction space and of said cavity ,resonators1g being parallel to the central axis of ,said bldck, wl1ichblock also has a plurality of couplihg'slots each interconnecting one of said .r cavity resonatorswith said interaction space, and

has a. tuning slot which is open at its two ends andis bounded by only, two surfaces of said block,

said surfaces being parallel with each other and with thecentral axis of said block, said tuning slot ff'o'rniing' a parallel plate transmission line for ''ele ctr'omagnetic waves of the operating frequency of said resonator device, 'sa'id tuning slot extending from endto end of said block and'from the interior of 'oneof said cavity resonators outwardly through" the outer surface-*of said block, and a tuning bridge slidably' mounted between the two plates bf said parallel plate transmission line.

2. A "tunable cavity resonator device in' accordancewith clair n' Landin'whichthe surfaces of said'block bounding 'the'said tuning slot are flat,

and parallel to a radial plane of the said{ cylindricalblock. I y

3; A tunable cavity resonator device in accord- 'li lceffwith c'la-im linwhiclithesurfaces organ block *boumling thesaid tuning slot'are'flatgp'arflallel to aradiafplaneof the'said cylindrical block and spaced apart a {distancesubstantiallyequal to the maximum inside diameterf of one of said cylindrical cavity resonators.

JOHN 'Cf" SLATER.

REFERENCES CITED The following references'are of record m the le, or this .patent:

. UNITED sTAa'EsPA'rENTs 

